Field Of The Invention
The present invention relates to explosive charges, more particularly to accessory charges for use in conjunction with explosives generally referred to as booster or primer explosives and to combinations of such accessory charges with such booster charges. Such combinations are intended primarily for use within boreholes and the like to initiate detonation of a larger mass of relatively insensitive explosive.
Related Art
U.S. Pat. No. 4,938,143 issued Jul. 3, 1990 to R. D. Thomas et al and entitled "Booster Shaped For High-Efficiency Detonating", discloses a booster explosive having an "interface" surface at one end which is configured to contact a column of a relatively insensitive explosive while being directed towards the majority of the insensitive explosives content of the column. The body portion of the booster has sides which taper to an opposite, second end thereof which second end has a cross-sectional area which is smaller than the interface end. While Thomas et al discloses a wide variety of such tapered shapes and illustrates many in the drawings, the preferred embodiment is shown in FIG. 5 of Thomas et al wherein the booster explosive has generally the configuration of a frustrum of a right angle cone. The Thomas et al booster is disposed at or near the bottom of a borehole filled with a mass of insensitive explosive, typically a blasting agent, with the base facing upwardly towards the major portion of explosive within the borehole. Commercially available embodiments of the Thomas et al invention are known in which a booster explosive shaped generally similar to that illustrated in FIG. 5 of Thomas et al is encased within a molded synthetic polymeric (plastic) container. As illustrated in FIG. 5 of Thomas et al, the frusto-conical shaped booster contains three bores formed therein, one of which comprises a dead-end passageway (152) within which a blasting cap (154) is inserted, another of which passageway (148) extends through the booster explosive for passage therethrough of its signal transmitting cord (156) to the surface. A third passageway (146) extends along the longitudinal center axis of the booster explosive and is stated to permit threading therethrough of the signal transmission cord of another detonator positioned in the borehole below the illustrated booster.